Left: five tubers from spring-planted crop. The tubers are small and, on the average, weigh 22 gr. The seed potatoes of this variant were cultivated in the Odessa district for seven years by the spring-planting method. Yield—1.5 tons per hectare. Right: five tubers from summer-planted crop. The tubers are large, average 470 gr. The first two years the seed potatoes were planted in the spring and the next five years in the summer. Yield—12 tons per hectare

The practical solution of the problem of combating the degeneration of potatoes in the South and the generalization of the mass experience of the collective farms have led to new discoveries, have increased our knowledge of plant life. It has been ascertained that the summer planting of potatoes, as a result of which the new tubers form under the cooler autumn conditions, not only keeps the tubers from degenerating, but alters the breed of the potato, not in the direction of degeneration, but in the direction of acquiring greater vigour. This has already been tested and proved for three years on large areas under collective-farm conditions. At our Institute we have had the same results for five years with the medium-ripening variety Ella, which A. F. Kotov, a specialist at our Institute, had taken for experimentation.

For four years, year after year, one variant of this potato was planted in the spring and another variant was planted year after year at the end of June and beginning of July. As a result, what seemed to be two distinctly different varieties were obtained. The first was a breed of potato that was good for nothing; the second was a variety that produced a good crop of large tubers. There can be no doubt that an alteration in the breed (genotype) took place here, for how otherwise is it possible to explain the different behaviour of the plants of these two variants when planted in the spring of 1937 under equal conditions? They produced different yields and tubers of different sizes and shapes; and the plants of these two variants bore stems and leaves of different appearance and vigour.

A. F. Kotov conducted a second experiment in altering the breed of potatoes in conformity with the conditions of cultivation. In the autumn of 1935 he took the crop of individual plants of the Early Rose variety, which had been planted in July. The total number of plants selected in 1935 was about three hundred. The crop from each plant, ranging from 5 to 10 tubers, was kept separately. In 1936, half the crop of each plant was planted in the field in spring; the other half was planted at the end of June. In the autumn of the same year the crop was harvested both from the spring- and from the summer-planted tubers. In the spring of 1937 tubers from the spring-planted 1936 crop were planted in the field, and next to them were planted tubers taken from the same plant (1935 selection), but grown from the 1936 summer planting. In the spring and summer of 1937 this experiment presented a magnificent picture. From the appearance of these 300 descendants one could easily tell which of them had come from the tubers grown from the previous year's spring planting, and which from the summer planting. In many cases the crop from plants obtained from the tubers of the 1936 summer planting was two or three times s large as that of plants from the same clone, the seed potatoes of which had been obtained from the 1936 spring planting.

In order to prevent them from degenerating as a result of the spring planting of 1937, Kotov took some of the tubers from the twelve best clones and planted them this year in the summer apart from those he planted in the spring. For the purpose of comparison, tubers from the same clones of last year's spring-planted crop were planted in the summer. Thus, it is possible to compare the crops of four variants obtained from one and the same plant, as is evident from the following table:

AVERAGE CROP FROM ONE POTATO PLANT DEPENDING ON PRECEDING CONDITIONS
OF CULTIVATION OF PLANTING MATERIAL

No. of Initial
Plant of 1935
Selection

1937 Spring Planting of Tubers from

1937 Summer Planting of Tubers from

Spring Planting 1936

Summer Planting 1936

Spring Planting 1936

Summer Planting 1936

Crop
in Grams

Number
of Tubers

Crop
in Grams

Number
of Tubers

Crop
in Grams

Number
of Tubers

Crop
in Grams

Number
of Tubers

59

153

5

315

9

513

6

847

8

82

247

6

373

6

320

4

606

9

105

126

4

263

5

353

5

740

7

181

205

8

450

9

363

4

800

6

203

45

6

408

9

364

8

713

9

213

82

6

173

6

440

5

747

7

221

87

8

250

14

413

8

820

10

224

208

6

320

7

440

6

527

6

232

83

5

413

7

260

4

933

11

244

212

10

443

15

420

5

547

7

265

42

5

538

11

407

6

727

5

From the table it is easy to see that:

1. Summer planting resulted in a much larger crop per plant and in larger tubers than spring planting. This is observed in plantings of tubers from the summer planting and in those of tubers from the spring planting of the preceding year.

2. With summer planting we got a more productive breed of seed potato.

The above results of Comrade Kotov's experiments show how sensitive the varietal nature of potato plants is to altered conditions of cultivation. It is extremely important to know this not only to prevent standard seed potatoes from deteriorating, but also to improve them from year to year, by noting and choosing the best conditions for growing them.

We have already observed that in the southern districts summer planting yields considerably better and healthier seed potatoes than spring planting. It is now necessary to examine this in greater detail. It is necessary experimentally to determine the different dates of summer planting of potatoes for the different districts of the South of the U.S.S.R. and for the different varieties. We must also learn to create such conditions for growing planting material as will produce the best breeds for spring planting in our districts with the object of obtaining young potatoes for food, and for summer planting with the object of obtaining planting material and market potatoes for autumn and winter and early spring consumption.

All that I have said about altering the breed of potatoes in conformity with conditions of cultivation is already known to many collective-farm laboratory managers from the work they themselves have done. Nevertheless, some scientists who espouse the principles of the old agronomics, the principles of the old genetics, are still convinced that conditions of cultivation play no role, or almost no role, in altering the nature of plant organisms. Such views on plant life and development not only made it difficult for these scientists to solve the problem of combating the degeneration of potatoes in the South, but today, when this problem is already solved, prevent, some of them from understanding the crux of the matter.

Quite recently a highly-skilled research worker submitted for publication, in a mass edition for the enlightenment of leading collective farmers, a manuscript in which he wrote things about the growing of seed potatoes that cannot be taken seriously today. According to this author, a variety well known to collective farmers, namely, Early Rose, though cultivated for 75 years in different zones of the globe, has not suffered any substantial change. This means that everywhere this variety has remained the same as it was 75 years ago. Something has prevented this author from learning even in 1937 that growing the Early Rose variety under spring or summer conditions in our districts fundamentally alters its breed in literally 3 months, let alone 75 years.

In this same manuscript the author said that varieties of potatoes, chiefly old ones that were bred a long time ago, degenerate for reasons unknown to science. This is not true. Not only are the reasons for degeneration of potatoes well known to every collective farmer, at any rate in the southern districts of the U.S.S.R., and particularly to collective-farm laboratory managers, but they are already being eliminated by means of summer planting.

The changes in the "breed" of potatoes described above may be attributed to phenotypic plasticity, as the phenomenon is now called.

The same same phenomenon had been observed in the U.S., but the remedy employed was not as satisfactory as what Lysenko described. Corbett (1907) wrote:

If we find these differences among plants grown from buds and cions, quite as marked peculiarities may be anticipated in plants grown from cuttings. Upon this point recorded observations are exceedingly meagre, but some light can be gathered from the work published by myself in the Ninth Annual Report of the West Virginia Agricultural Experiment Station. From these studies it is evident that varieties are perpetuated true to type by cuttings through many generations. A single exception in the case of the tomato entering to break the constancy of the results. Not only are general varietal differences retained, but acquired characters also, temporarily, at least, as is shown in the cuttings of grape, poplars, currants, etc., grown in Northern and Southern latitudes. For a specific example of this, nothing could be more conclusive than the results shown by New York grown potatoes, given one season's outing in Maine, for, when brought back to New York the next year, they retained their Maine tendency towards increased vigor and yield.

Cold stress induced severe demethylation in core regions but left linker regions relatively intact. Thus, methylation and demethylation were periodic in nucleosomes. The following biological significance is conceivable. First, because DNA methylation in nucleosomes induces alteration of gene expression by changing chromatin structures, vast demethylation may serve as a common switch for many genes that are simultaneously controlled upon environmental cues. Second, because artificial demethylation induces heritable changes in plant phenotype, altered DNA methylation may result in epigenetic inheritance, in which gene expression is modified without changing the nucleotide sequence.

Our cultivated potatoes are descended from Andean ancestors, and retain many of their ancient adaptations. If cold stress can cause changes in methylation, it is not unreasonable that excessive heat might do the same thing in potatoes where production of tubers in cool weather is really to be expected. It would be interesting to learn whether late planting of other Andean geophytes would bring similar benefits.

T. A. Knight (1814) also found that late planting of potatoes revived a degenerated strain, and increased the size of tubers 10-fold.

Corbett, L. C. (1907). Improvement of Roses by Bud Selection or Blind vs. Flowering Wood for Rose Cuttings. Horticultural Society of New York Memoirs:
International Conference on Plant Hardiness and Acclimatization.http://www.bulbnrose.org/Roses/breeding/vegselec.htm